Previous research suggests that Vitamin C depletion modifies energy expenditure and, in particular, fat oxidation. Also, impaired fat oxidation has been implicated in the development of obesity and in failed weight loss attempts. The purpose of this study was to assess the effect of Vitamin C (VC) supplementation on fat kcal utilization during a 60 min walk at 50% maximal oxygen consumption using a randomized, double-blind, placebo-controlled, 4-week trial in obese men and women.
METHODS: Apparently healthy obese (BMI >30 kg/M2) men (n=4) and women (n= 11) (mean age: 34 ±11 years) unaware of their vitamin C status agreed to participate. Subjects were provided food for an energy restricted and vitamin C poor (∼ 40 mg day) diet and randomly assigned to either placebo (PL; n=8) or vitamin C (VC; 500 mg/d; n=8).
RESULTS: After 4 weeks of diet adherence, plasma vitamin C concentrations increased in VC (0.841 ± 0.034 and 1.089 ± 0.148 mg/dL for weeks 0 and 4 respectively) and decreased in PL (0.732 ±0.108 and 0.538 ± 0.117 mg/dL) (p < 0.001 for time × group effect). Body mass was reduced significantly (p < 0.001, time effect only): −4.1 and −4.3 kg in VC and PL, respectively. Body fat mass decreased in both groups, but this reduction approached significance only for VC (−1.7 kg; p=0.077). No significant differences (p > 0.05) were noted between groups during the 60 minute walk in energy expenditure (kcal/min), relative percent of VO2 max (51 ± 1.0%), mean work rate (kgm/min) or mean heart rate (bpm). However, mean RER for minutes 40–60 was 0.78 ± .04 for VC and 0.81 ± .05 for PL creating a trend (p = 0.077) for the contribution of fat kcal/min to be higher in VC vs. PL: 6.06 ± 1.1 vs. 4.8 ±1.1 kcal/min.
CONCLUSIONS: These preliminary data suggest that vitamin C status may influence fat oxidation during prolonged moderate walking in obese individuals on a calorie-restricted diet. This research was supported by a grant from the General Mills, Bell Institute of Health and Nutrition.